1. Field of the Invention
This invention relates to a novel substituted fluorine-containing .beta.-indolebutyric acid compound having a physiologically active capacity for markedly elongating plant roots, a plant growth regulating agent containing the substituted fluorine-containing .beta.-indolebutyric acid compound as an active component thereof, and a method for regulating the length of roots sprouting from plant seeds and the length of hypocotyls by the action of the compound.
2. Description of the Prior Art
It has long been known that indole-3-acetic acid (hereinafter referred to as "IAA") and derivatives thereof such as, for example, methyl indole-3-acetate and indole-3-acetamide, accelerate the growth of plants. It is also known that 4,7-dichloroindole-3-acetic acid and 5,7-dichloroindole-3-acetic acid manifest an anti-auxin action ["Planta," Vol. 140, page 89 (1978)].
It has been recently ascertained that 4,4,4-trifluoro-3-(indole-3-)butyric acid (hereinafter referred to as "TFIBA"), 4,4,4-trifluoro-2-hydroxy-3-(indole-3-)butyric acid ("TFIHBA"), and 4,4,4-trifluoro-3-(indole-3-)butyronitrile ("TFIBN"), which are fluorine-containing .beta.-indolebutyric acid compounds, manifest a strong activity in accelerating the growth of plant roots (Collection of monographs for publication at the 1990 general meeting of Plant Chemical Regulation Society, page 31, published by Plant Chemical Regulation Society). In Japanese Patent Public Disclosure Hei 5(1993)-279331, some of the present inventors have disclosed fluorine-containing indolebutyric acid compounds which manifest a similar effect.
In the recent years, increasing the yield of plants which are useful as food has become an important task in view of the growth of the world's population. The acceleration of the elongation of plant roots is one of the factor necessary for increasing plant yield. Plant growth regulating agents containing such compounds as IAA and exhibiting anti-auxin activity and other conventional plant growth regulating agents are, however, not sufficiently active in elongating plant roots. The TFIBA, TFIHBA, and TFIBN mentioned above are fluorine-containing .beta.-indolebutyric acid compounds that exhibit fairly strong plant root elongation activity, as compared with IAA and the derivatives thereof. Nevertheless, their activity is not fully satisfactory for practical use. A need exists for developing a substance capable of exhibiting even stronger plant root elongation activity.